1. Field of the Invention
The present invention relates generally to a shock absorber, such as that suitable for use in an automotive suspension system. More specifically, the invention relates to an improved construction of a piston assembly of the shock absorber.
2. Description of the Background Art
One of the general constructions of hydraulic shock absorbers has been disclosed in Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 60-52438. In the shown construction, a thrusting piston is disposed within a fluid chamber defined in a cylinder filled with a working fluid. The piston is firmly secured on an inner end of a piston rod which extends through the cylinder. The piston rod has a stud section at the end engaged to the piston. The stud section is provided a smaller diameter than that of the major section of the piston rod. The piston engages with the stud section and firmly secured thereon by means of a fastening nut.
It is generally technology for providing satisfactorily high wear resistance for the major portion of the piston rod, which thrustingly moves along the axis of the cylinder with sliding contact with the end plug. Wear resistance is usually provided by induction hardening. When induction hardening is made for the end portion of the piston rod where the stud section has to be formed, machining becomes difficult. As a result, it is required to limit portion to perform hardening operation and to manage di-rectionality of the piston rod. This causes higher production cost. Furthermore, when a leaf spring valve is used for controlling fluid flow through the piston, a valve collar becomes necessary for avoiding interference or collision between the thread in the stud section and the inner peripheral edge of the leaf valve spring.